This invention relates to methods for inhibition of growth of transformed cells, and inhibition of progression to a transformed phenotype in pre-neoplastic cells.
Transformation is a cumulative process whereby normal control of cell growth and differentiation is interrupted, usually through the accumulation of mutations affecting the expression of genes that regulate cell growth and differentiation.
Scanlon WO91/18625, WO91/18624, and WO91/18913 describes a ribozyme effective to cleave oncogene RNA from the H-ras gene. This ribozyme is said to inhibit H-ras expression in response to exogenous stimuli. Reddy WO92/00080 describes use of ribozymes as therapeutic agents for leukemias, such as CML by targeting specific portions of the BCR-ABL gene transcript.
The platelet derived growth factor (PDGF) system has served as a prototype for identification of substrates of the receptor tyrosine kinases. Certain enzymes become activated by the PDGF receptor kinase, including phospholipase C and phosphatidylinositol 3' kinase, Ras guanosine triphosphate (GTPase) activating protein (GAP) and src-like tyrosine kinases. GAP regulates the function of the Ras protein. It stimulates the GTPase activity of the 21 kD Ras protein. Barbacid. 56 Ann. Rev. Biochem. 779, 1987. Microinjection of oncogenically activated Ras into NIH 3T3 cells induces DNA synthesis. Mutations that cause oncogenic activation of ras lead to accumulation of Ras bound to GTP, the active form of the molecule. These mutations block the ability of GAP to convert Ras to the inactive form. Mutations that impair the interactions of Ras with GAP also block the biological function of Ras.
While a number of ras alleles exist (N-ras, K-ras, H-ras) which have been implicated in carcinogenesis, the type most often associated with colon and pancreatic carcinomas is the K-ras. Ribozymes which are targeted to certain regions of the K-ras allelic mRNAs may also prove inhibitory to the function of the other allelic mRNAs of the N-ras and H-ras genes.